USBC Rule 4a - Legal Delivery
A delivery is made when the ball leaves the player’s possession and crosses the foul line into playing territory. Every delivery counts unless a dead ball is declared. (See Rule 8.) A delivery must be made entirely by manual means. No device may be incorporated in or affixed to the ball that detaches on delivery or is a moving part during delivery except as provided in Rules 4b and 4c.
** I've searched through the rule book and there is no rule that addresses a 2 handed delivery because there is no way that USBC could say a 2 handed delivery is a illegal delivery (YET).
I've only seen Jason Belmonte bowl and unless his version of the 2 handed delivery is different, "at the point of release," only his right hand is on the ball. Just before release, his left hand/arm acts just as it does for all bowlers and acts as a normal balance arm. With a 2 handed delivery, when the balance hand/arm goes into motion, the 2 handed bowler would get more torso rotation, which would give him/her an extra advantage with ball speed.
I'm sure a 2 handed bowler could fight this at that house, and most likely win. This reminds me back in the day, when mixed leagues would try to deny an all women's team from bowling, and the women's team would protest, based on discrimination, then the leagues would always back off. I realize this is a differnt topic, but along the same lines.
So, what's next? No backup ball? No palm ball? No between the legs shot?